Cutting blade hard-facing method and apparatus

ABSTRACT

A hard-faced cutting blade and hard-facing method is provided. A hard-facing material is applied to a cutting edge of a cutting blade such that a heat-affected transition zone may be created between the base metal and the hard-facing material. The heat-affected transition zone may create a sufficient bond to help resist delamination and flaking of the hard-facing material from the base metal.

FIELD OF THE INVENTION

Disclosed embodiments of the invention relate to the field of cuttingblades, and more particularly, embodiments of the invention relate to ahard-faced cutting edge that may be used in environments such as lawn,garden, agricultural, and forestry applications.

BACKGROUND OF THE INVENTION

It is important for cutting blades, including but not limited to rotarycutting blades, to maintain a sharp and durable cutting edge throughoutthe life of the blade. One technique that has been used to increase thewear resistance of the cutting edge is to apply a layer of a hardermaterial to the surface of the cutting blade that will resist wear.Often referred to as hard-facing, a number of different techniques existfor performing such an operation.

Some hard-facing methods involve mixing a powdered metal alloy withcertain solvents to form a slurry, which is then applied to the metalsurface of the cutting blade. The blade is then heated to cause themetal alloy to adhere to the metal of the cutting blade. Otherhard-facing techniques include high velocity oxygen formation (HVOF).HVOF typically includes injecting the hard-facing metal alloy in powderor solid form into a high temperature high velocity flame. The flameaccelerates the metal particles toward the metal blade and melts thehard-facing onto the surface of the base metal.

Though these hard-facing processes result in cutting blades havingextended wear surfaces, they have several deficiencies, including, butnot limited to, an unreliable bond created between the hard-facingmaterial and the cutting blade base metal such that the hard-facing isprone to delaminating, chipping, or flaking during operation; theprocesses involved can impact the overall heat treatment of the cuttingblade and therefore negatively impact the blade characteristics, such asmaking the blade more brittle and prone to cracking or shattering; andthese processes are often expensive, laborious and can generate asubstantial amount of waste material, which may be hazardous in nature.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments in accordance with the present invention are illustrated byway of example and not by way of limitation in the figures of theaccompanying drawings, in which the like references indicate similarelements and in which:

FIG. 1 illustrates a perspective view of a cutting blade in accordancewith an embodiment of the present invention;

FIG. 2 illustrates an enlarged cross-sectional view of a cutting bladein accordance with an embodiment of the present invention; and

FIGS. 3A and 3B illustrate a 200× magnification of partialcross-sectional comparison views of a cutting blade having a hard-facingin accordance with the present invention and a cutting blade having acurrent hard-facing.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

In the following detailed description, reference is made to theaccompanying drawings which form a part hereof wherein like numeralsdesignate like parts throughout, and in which is shown by way ofillustration specific embodiments in which the invention may bepracticed. It is to be understood that other embodiments may be utilizedand structural or logical changes may be made without departing from thescope of the present invention. Therefore, the following detaileddescription is not to be taken in a limiting sense, and the scope of thepresent invention, and embodiments in accordance therewith is defined bythe appended claims and their equivalents.

Embodiments in accordance with the present invention provide a cuttingblade, such as a rotary cutting blade, that has a hard-facing materialapplied to at least one surface of a cutting edge, wherein aheat-affected transition zone exists between the hard-facing materialand the base metal of the cutting blade. The heat-affected transitionzone may be an area where molecules of the hard-facing material maypartially mix with the molecules of the base metal to provide anincreased bond therebetween. Embodiments in accordance with the presentinvention may provide a hard-facing surface sufficiently bonded to thebase metal of the cutting blade, such that chipping, delamination, andother negative effects encountered by current hard-facing blades aresignificantly reduced.

In one embodiment in accordance with the present invention, a rotarycutting blade includes a beveled cutting edge on opposite ends andopposite edges of the rotary cutting blade. A hard-facing material maybe applied to the non-beveled edge portion in accordance withembodiments of the present invention. The beveled edge of the base metalmay wear away at a faster rate than the edge having the hard-facingmaterial applied thereto, which in turn may result in the cutting edgemaintaining a sharp edge through a longer period of operational life.This not only may reduce the length of time between sharpening of thecutting edge, but also may increase the wear life of the rotary cuttingblade.

Embodiments in accordance with the present invention include methods forapplying a hard-facing material, such as tungsten carbide to cuttingedge without dramatically affecting overall strength or toughness of theblade. One embodiment in accordance with the present invention, a rotarycutting blade having a hard-facing material applied to a cutting edgeincreases the wearability of the cutting blade, but does not cause theblade to become brittle such that it can fail standardized impacttesting required for certain cutting blade applications.

FIG. 1 illustrates a perspective view of a cutting blade in accordancewith an embodiment of the present invention. Blade 10 may have a firstend 12 and a second end 12′, and a first side 14 and a second side 14′.Each end 12, 12′ may have a cutting edge 16, 16′. Cutting edge 16 mayconsist of a second side beveled edge portion 18 and first sidenon-beveled edge portion 20. As the embodiment of the present inventionillustrated in FIG. 1 uses a rotary cutting blade by way ofillustration, it can be appreciated that the second end 12′ of thecutting blade may have the same features and characteristics as that ofthe blade on the first end 12, but will not be expressly detailedherein.

A hard-facing applicator 22 may be used to apply a hard-facing material26 to the non-beveled edge portion 20. Hard-facing applicator 22 mayinclude a hard-facing material source 24, shown in the form of aconsumable disk comprised of the hard-facing material 26. Hard-facingapplicator 22 may be an electrically controlled device adapted to spinthe disk in an annular fashion to prevent flat spots from being worninto the consumable disk 24. Hard-facing applicator 22 may also beadapted to move linearly in a substantially parallel direction with thenon-beveled edge portion 18, as shown by movement arrows 28. Hard-facingapplicator 22 may also be adapted to move perpendicularly to thenon-beveled edge portion 18, as shown by directional arrows 29, to allowthe consumable disk 24 to step to an untreated portion of thenon-beveled edge. This can enable the user to achieve the desired widthof hard-facing on the cutting blade, and/or may allow the applicator toapply more hard-facing material from consumable disk 24 in a particulararea of non-beveled edge 20.

Hard-facing applicator 22 may be coupled to an electricity source 25,which may include any suitable voltage-generating device, and adapted toselectively and controllably supply voltage to disk 24. Cutting blade 10may be electrically coupled to a ground or complementary voltage source27, such as a negative voltage source. Cutting blade 10 then may act asan cathode and the consumable disk 24 may act as an anode (when coupledto electricity source 25), for example. In one embodiment, when avoltage is supplied to the disk 24, an arc may be generated between thedisk 24 and the base metal of cutting blade 10 as current i flows fromthe anode to the cathode. This arcing action may cause the hard-facingmaterial 26 to be deposited onto the non-beveled edge portion 20. Thearcing action may also cause the hard-facing material of disk 24 tosufficiently bond with the base metal of cutting blade 10 through thecreation of a heat-affected transition zone.

The hard-facing applicator 22 may be moved along the non-beveled edgeportion 20 of the cutting edge 16 to deposit a layer of hard-facingmaterial 26 along as much of the cutting edge 16 as is desired.Hard-facing applicator 22 may also move perpendicularly to step the disk24 to a portion of the non-beveled edge portion 20 of the cutting edge16 that has not had hard-facing material 26 yet applied. The hard-facingapplicator may also be adapted to adjust the positioning of theconsumable disk 24 with relation to the non-beveled edge portion 20 toallow the arcing action to occur, even as the disk is consumed. Rotationof the disk and linear movement 28 may prevent the consumable disk fromstaying in one position too long such that the consumable disk 24 weldsto the non-beveled edge portion 20. This may also allow the consumabledisk 24 to wear in a substantially uniform fashion.

It can be appreciated that the width and length of the hard-facingmaterial 26 that is deposited may be controlled as desired depending on,for example, the blade size and configuration, or may be depositeddepending on the portions of the blade that see the greatest amount ofwear during operation, or based on other empirical factors. The depth ofthe hard-facing material 26 can vary. It has been found that depthsranging from 0.0004″ to 0.005″ in rotary cutting blade applications issufficient to result in a heat-affected transition zone that may ensurea substantial bond between the hard-facing material and the base metal.It can be appreciated, however, that the overall depth of thehard-facing material may change depending on the application for thecutting blade.

In one embodiment in accordance with the present invention, it has beenfound that pulsing current i through the disk 24 at a rate in the rangeof 10 to 60 amps, may allow for a sufficient application of hard-facingmaterial 26. Further, it has been found that cycling these pulses ofcurrent in a range of 50 to 400 Hertz may be sufficient to apply thehard-facing material 26 without overheating the blade, and/or causingcertain blade characteristics, such as strength and toughness, to changeand adversely impact the ability of the blade to meet certain impactstandards.

In one embodiment in accordance with the present invention, the currenti is not pulsed, but may be substantially maintained at a constantstate. In such a case, the temperatures of the base metal may tend torise higher and maintain elevated temperatures longer, which may,depending on the characteristics of the base metal, impact the strengthand toughness of the blade.

Cutting blade 10 may include a base metal consisting of a carbon steelthat may be typically used for cutting blade operations, with the carboncontent and heat treatment modified such that the blade may achieve adesired hardness and toughness/strength suitable for the intendedoperation. Other carbon steel alloys may be used, including, but notlimited to, boron steel and titanium steel. In many cutting bladeapplications, such as rotary cutting blades, hardness and toughness aretwo of the primary concerns. Hardness is typically used as a measure ofthe material's resistance to wear, where toughness or strength may beused as a measure of the blade's brittleness, e.g; its ability to resistfracturing, cracking when an object is encountered.

Achieving a certain strength and toughness of the cutting blade iscritical to the extent that certain regulatory bodies require thecutting blade strength to be such that impact of the cutting blade witha solid objects will not cause the cutting blade to break or fracture,such that people may be harmed by the fracturing pieces. For example,rotary cutting blades may be subject to many standards, such as theAmerican National Standards Institute (ANSI) B 71.1 for walk behindmowers and ride-on machines with mowers, and the American Society ofAgricultural Engineers (ASAE) S474, which governs agricultural rotarymower safety. These tests both involve inserting a steel stake into therotating path of the rotary blade to evaluate what happens to thecutting edge of the blade when it impacts the metal stake. Bothstandards have requirements for scenarios that can cause the blade tofail the test, including but not limited to blade fracture, excessivechipping, and the like.

Hard-faced blades in accordance with embodiments of the presentinventions may result in an increased hardness (i.e., wear resistant)blade that has a heat-treated strength such the toughness is notadversely altered by the hard-facing process such that it would renderthe blade unable to pass the tests set forth in the various standards.

Hard-facing material 26 may be any one of a variety of metal alloys thatare known to have higher hardnesses, including but not limited totungsten carbide, tungsten carbide having a cobalt content, boroncarbide, nickel bonded carbide, stellite, and a variety of others metalalloys. In one embodiment in accordance with the present inventions, thehard-facing material 26 may be a tungsten carbide having a 6% cobaltcontent.

FIG. 2 illustrates an enlarged cross-sectional view of a cutting bladein accordance with an embodiment of the present invention. Blade 10 hasa hard-facing material 26 bonded to a first side 34 of the base metal 36of cutting blade 10, and an overall thickness 38. As the hard-facingmaterial 26 is deposited on the first side 34 of blade 10 in accordancewith embodiments of the present invention, the arching action may causea dramatic increase in the localized temperature at the first side 34 ofbase metal 36. The increased temperature may have several effects on therotary cutting blade 10. One effect is that some of the molecules of thefirst surface 34 of base metal 36 may mix with the molecules ofhard-facing material 26 thereby creating a heat-affected transition zone32. Upon cooling, the heat-affected transition zone 32 may result in asufficiently increased bond between hard-facing material 26 and the basemetal of blade 10.

Another effect is that the metallurgical structure of the alloy maychange such that the hardness and toughness of the blade may be altered.It has been found that the increase in heat results in the heat-affectedtransition zone has a hardness greater than that of the base metal butless than that of the hard-facing material. It has also been found thatthe heat-affected transition zone does not adversely impact thetoughness of the blade such that it would fall below acceptablestandards. The heat-affected transition zone and the bond associatedtherewith, may help the hard-facing material 26 resist flaking,chipping, or delaminating from the base metal of blade 10, both duringnormal operation as well as during abnormal incidents, such as therigors imposed by various standardized testing requirements.

Heat-affected transition zone 32 may make up a relatively thin portionof the overall thickness 34 of the cutting blade 10 and may becontrolled by the magnitude of current that is pulsed through the bladeand the frequency of the pulses. It has been found that using too muchcurrent, or overextending the pulse duration may cause the heat-affectedtransition zone to increase in thickness and negatively impact theoverall blade characteristics of the cutting blade 10, such as reducingstrength and toughness. In one embodiment in accordance with the presentinvention, the thickness of the heat-affected transition zone may beless than 5% of the overall thickness 38 of the cutting blade 10. Inanother embodiment, the thickness of the heat-affected transition zonemay be less than the thickness of the hard-facing material. It can beappreciated, however, that the thickness of the hard-facing materialapplication can be adjusted to meet the needs of the operation in whichthe cutting blade is being used.

FIGS. 3A and 3B illustrate a 200× magnification of a partialcross-sectional comparison view of a cutting blade having a hard-facingin accordance with the present invention and a hard-facing known in theart, where the cross sectional blade pieces have been polished andsubjected to a Nital etch. FIG. 3A is a photograph of a cross section ofcutting blade in accordance with the present invention. Heat-affectedtransition zone 32 is disposed between hard-facing material 26 and basemetal 36. FIG. 3B is a photograph of the cross section of a cuttingblade 50 with a hard-facing material 52 as applied using a known method.No discernable heat-affected transition zone exists between the basemetal 56 and the hard-facing material 52. Accordingly, the hard-facing52 is prone to delaminate, chip, or separate at interface 54 duringoperation, and particularly where an object is encountered.

As illustrated in FIG. 3A, the hard-facing material 26 need not beevenly deposited across the surface of the cutting blade to beeffective. Rather, it has been found that the obtaining a coverage of50% or greater of hard-facing material along the length of the cuttingedge may be sufficient to significantly increase the wear life of acutting blade and result in an increased tendency for the cutting edgeto remain sharp. It can be appreciated, however, that a less than 50%hard-facing material coverage may still achieve increased wear andresult in the cutting edge maintaining a sharp edge longer than acutting blade that does not have a hard-facing in accordance with thepresent invention.

As shown in FIG. 3B, the hard-facing surface 52 is relatively uniformlydeposited across the cutting edge of the cutting blade. Achieving suchuniformity is unnecessary with blades having the heat-affectedtransition zone. It can be appreciated, however, that the moreconsistent the coverage of the hard-facing material is across thecutting edge, the better the stay-sharp characteristics of the blade maybe over the operational life of the blade.

In one embodiment in accordance with the present invention, thehard-facing material may be applied to the beveled edge portion of thecutting blade. In another embodiment in accordance with the presentinvention, hard-facing material may be applied to both the non-bevelededge portion and the beveled edge portion of the cutting edge. It canalso be appreciated that though the cutting edge shown in theillustrated embodiments includes only one beveled edge to define thecutting edge, both edges may be beveled to define the cutting edge.

Embodiments in accordance with the present invention may be applied to avariety of cutting blade applications where it is important to maintaina certain strength and toughness, including, but not limited to, rotarycutting blades, such as lawnmower blades, reel-type mower blades, aswell as teeth on a wood-cutting saw. Further, it can be appreciated thatin accordance with embodiments of the present invention, the hard-facingmaterial my be deposited using a hard-facing material source in formsother than disk form, such as a rod, billet, and the like.

Although specific embodiments have been illustrated and described hereinfor purposes of description of the preferred embodiment, it will beappreciated by those of ordinary skill in the art that a wide variety ofalternate and/or equivalent implementations calculated to achieve thesame purposes may be substituted for the specific embodiment shown anddescribed without departing from the scope of the present invention.Those with skill in the art will readily appreciate that the presentinvention may be implemented in a very wide variety of embodiments. Thisapplication is intended to cover any adaptations or variations of theembodiments discussed herein. Therefore, it is manifestly intended thatthis invention be limited only by the claims and the equivalentsthereof.

1. A cutting blade, comprising: a base metal having a cutting edgeformed therein; a hard-facing material disposed on at least a portion ofat least one side of the cutting edge; and a heat-affected transitionzone between the at least one side of the cutting edge and thehard-facing material such that the cutting blade resists delamination ofthe hard-facing material.
 2. The cutting blade of claim 1, wherein thebase metal has a first toughness and the hard-facing material has asecond toughness that is greater than the first toughness, and theheat-affected transition zone having a third toughness that is betweenthe first and second toughness.
 3. The cutting blade of claim 1, whereinthe heat-affected transition zone is caused by a mixing of molecules ofthe hard-facing material with molecules of the base metal.
 4. Thecutting blade of claim 1, wherein the cutting edge is defined by abeveled edge portion and a non-beveled edge portion, the hard-facingmaterial being applied to the non-beveled edge portion.
 5. The cuttingblade of claim 4, wherein the cutting blade is a rotary cutting bladeand the non-beveled edge portion is oriented facing a material beingcut.
 6. The cutting blade of claim 1, wherein the cutting blade has anoverall thickness, and the heat-affected transition zone comprises lessthan 5% of the overall thickness.
 7. The cutting blade of claim 1,wherein the hard-facing material is deposited such that it covers morethan 50% of the surface of the cutting edge to which the heat-affectedtransition zone is applied.
 8. The cutting blade of claim 1, wherein thecutting blade is a selected one a group consisting of a rotary cuttingblade, reel-type mower blade, and a saw chain cutting tooth.
 9. Thecutting blade of claim 1, wherein the hard-facing material is a selectedone a group consisting of a tungsten carbide, tungsten carbide withcobalt, boron carbide, nickel-bonded carbide, and stellite.
 10. A methodfor hard-facing cutting blades, comprising: providing a cutting bladehaving a cutting edge; providing a hard-facing applicator coupled to ahard-facing material source; coupling the hard-facing applicator to avoltage source; moving the hard-facing material source across thecutting edge such that the hard-facing material source passes in closeproximity to the cutting edge; passing a current through the hard-facingmaterial source to create an arc between the cutting edge and thehard-facing material source; and depositing the hard-facing material onthe cutting edge.
 11. The method of claim 10, wherein the hard facingmaterial source is a consumable disk, and further comprising: rotatingthe consumable disk as it passes along the cutting edge; and steppingthe location of the disk as needed to obtain a desired width ofcoverage.
 12. The method of claim 10, wherein passing current throughthe hard-facing material source includes pulsing current through thehard-facing material source.
 13. The method of claim 12, wherein pulsingcurrent further includes modifying the frequency and magnitude of thepulses to prevent the cutting blade from heating up to the point wherethe strength characteristics are changed such that the cutting bladewould not pass standardized testing requirements.
 14. The method ofclaim 12, wherein pulsing current through the hard-facing materialsource includes pulsing current in the range of 10 to 60 amps at afrequency in the range of 50 to 400 Hertz.
 15. The method of claim 10,wherein the cutting edge is defined by at least one beveled edge portionand one non-beveled edge portion, and wherein depositing the hard-facingmaterial on the cutting edge includes depositing the hard facingmaterial on the non-beveled edge portion.
 16. The method of claim 10,wherein depositing the hard-facing material on the cutting edge includesdepositing hard-facing material on at least 50% of the surface area ofthe cutting edge.